Conjugated polymers in electrophotography

ABSTRACT

Poly-2,9-methylenefluorene, fully conjugated via 9methylenefluorene repeating units, has been found to be a useful photoconductor in electrophotographic processes.

United States Patent [191 Bauer et al.

[ 1 CONJUGATED POLYMERS IN ELECTROPHOTOGRAPHY [75] Inventors: Wolfgang G. Bauer, Korntal,

Germany; Ulrich T. Mueller-Westerhoff, Monte Sereno, Calif.

[73] Assignee: International Business Machines Corporation, Armonk, NY.

[22] Filed: Feb. 20, 1973 [21] Appl. No.: 333,829

[52] US. Cl 96/15, 252/501, 260/67 R, 96/1.6 [51] Int. Cl. G03g 5/04, 603g 7/00 [58] Field of Search 96/].5; 252/501; 260/67 R [451 Feb. 12, 1974 Primary ExaminerRoland E. Martin, Jr. Assistant Examiner-J. P. Brammer [57] ABSTRACT Poly-2,9-methylenefluorene, fully conjugated via 9- methylenefluorene repeating units, has been found to be a useful photoconductor in electrophotographic processes.

4 Claims, No Drawings C ONJUGATED POLYMERS IN ELECTROPHOTOGRAPHY FIELD OF THE INVENTION This application is concerned with poly-2,9- methylenefluoreneand its use in electrophotography as a photoconductor.

PRIOR ART Photoconductive polymers have been known in the past, e.g., U. S. Pat. Nos. 3,037,861; 3,232,775 and 3,655,378. The polymer of the present invention, however, is different in chemical structure from any previously known.

SUMMARY OF THE INVENTION It has now been found that poly-2,9- methylenefluorene may be prepared by the basecatalyzed polycondensation of fluorene-2- carboxaldehyde. The equation for this reaction is as follows:

Poly-2,9-methylenefluorene can be dissolved in many organic solvents and can be dried as a layer on a support as a clear film. It has the mechanical properties desirable in film forming polymers to make it suitable for use in electrophotographic processes. To form photoconductive layers, the polymers of the present invention are dissolved in a suitable solvent such as tetra- 40 hydrofuran and coated by such methods as spray coating, dip coating, doctor blade, etc., onto a suitable substrate.

The photoconductive coatings can be chemically sensitized to increasethe level of sensitivity to light of a given wave length. Preferred sensitizing compounds for this purpose comprise 9-dicyanomethylene-2,4,7- trinitrofluorene, 2,4,7-trinitrofluorenone (TNF), 3,5- dinitrobenzoic acid, tetrachlorophthalic anhydride, tetranitronaphthalene, tetracyanoethylene 2,4,7-trinitrophenanthroquinone and related compounds. In general, the preferred sensitizers are electron accepting compounds, also known as Lewis acids.

There are several well known electrophotographic electrophotographic reproduction processes, however, involve the process step of selectively rendering portions of a photoconductor electrically conductive by selective exposure to light. The polymers of the present invention are very well suited for use in electrophotog raphy because of their photoconductivity and their desirable film forming characteristics. The preferred activator for each use, and the preferred amount thereof, are readily determined by routine testing.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in the form and details may be made therein without departing from the spirit and scope of the invention.

EXAMPLE I Preparation of poly-2,9-methylenefluorene To a suspension of potassium ethoxide in tetrahydrofurane (THF) prepared from 1.95 g (50 mmoles) potassium and 2.8 g mmoles) absol. ethanol in 10 ml absol. THF, a solution of 9.7 g (50 mmoles) flourene-Z-carboxaldeyde in 60 ml absol. THF was added at room temperature. After stirring this mixture for 48 hrs. the solution was filtered from 0.8 g THF- insoluble material. On addition of 500 ml ether to the yellow THF solution a yellow polymer precipitated, which was washed with water and ether, respectively. After vacuum drying and reprecipitation from methylene chloride/hexane 7.5 g of yellow polymer, no melting to 300C, slow darkening 300C, were obtained. GPC analysis gave the follwoing molecular weight distribution: M,,=1740, M,,,= 2380, M,,,/M,,=l.37. Calcd. for (C I-L 0). (C H L C 94.71 H 4.60 0 0.69 Found 94.36 4.76 NMR spectrum .e QIP iQn w w- W IR spectrum (KBr): 1715 cm C O 1620 cm Exocyclic C C l595 cm UV spectrum in CHCl 265,360 nm 7 EXAMPLE II The polycondensation product of Example I showed effective photoconduction properties together with good charge acceptance, especially in a negative mode, and especially with the addition of sensitizers. The following table summarizes the photoconductive and electrophotographic properties of the polymer, without and in CDCl;,:

with the activators 9-dicyanomethylene-2,4,7- trinitrofluorenone (DCMF) and 2,4,7- trinitrofluorenon (TN F):

System Negative Mode Positive Mode Charge T, Charge H, Acceptance (full) Acceptance (full) (I) no activator l50 V V (l) DCMF (|:0.5) 5.5 V 0.2 sec (1): TNF(1:l) 530v 0| 270v 0.7 sec reproduction processes in current use. They differ in the particular way in which they are carried out, particularly the sequence in which electric charging (usually with a corona) and illumination are carried out. All

The method of evaluation was:

a. a 10% by weight solution of (l) in THF was made, b. the activator, (DCMF) or (TNF), was added in the ratio noted in the table on a weight basis,

the photoconductor comprises poly-2,9- methylenefluorene.

2. A process as claimed in claim 1 wherein the photoconductor also comprises an electron accepting activator.

3. A process as claimed in claim 2 wherein the activator is 9-dicyanomethylene-2,4,7-trinitrofluorene.

4. A process as claimed in claim 2 wherein the activator is 2,4,7-trinitro-9-fluorenone.

* a: at 

2. A process as claimed in claim 1 wherein the photoconductor also comprises an electron accepting activator.
 3. A process as claimed in claim 2 wherein the activator is 9-dicyanomethylene-2,4,7-trinitrofluorene.
 4. A process as claimed in claim 2 wherein the activator is 2,4, 7-trinitro-9-fluorenone. 